1. Field of the Invention
The present invention relates to a local network of industrial or domestic type, for commanding and/or controlling several appliances by means of several distributed computers. The present invention more specifically relates to a system enabling the power supply of the appliances connected to the network via the network itself (remote power supply).
2. Discussion of the Related Art
It is generally necessary to supply each of the elements connected to a network, be it only to supply the interface circuits of these elements with the network. Most often, the network elements are not in a same casing, whereby each element has to be power-supplied individually, which increases the cost of the installation.
Telephone networks, for example, avoid this problem by a remote power supply of the telephone sets. However, a telephone network can only supply limited power due to the relatively high impedance of the lines and to the presence of line terminators.
There also exist so-called "carrier current" networks which convey information on the mains voltage which supplies the network elements. However, it is necessary to provide step-down transformers to supply the elements, which increases the cost and the bulk.
Another disadvantage of telephone or carrier current networks is that the information exchange rate is particularly low.
In high bandwidth networks, it could be devised to convey power on wires separated from those which carry the information. Such a solution however requires the use of specific cables and connectors which are thus much more expensive than those traditionally used in networks.
Further, providing additional wires increases the wiring error risks upon installation or repairing of the network, to such an extent that users prefer to supply the network elements individually.